Bi guy and full on wanker here. I really can't tell how common it is among straight dudes: maybe if I ever serve time in prison I'll give you a better informed answer!
I can say I though, I love the camaraderie of beating my meat with like-minded guys, it's always sexy but not always sexual. Perhaps that difference is an indicator of when straight guys have been present??
You maybe best starting a thread in the Zoomers lounge forum, as that really took off as a Covid thing, when guys could hold virtual jacking meets. So a lot of the visitors are gonna be men who do or would like to wank with buddies. I take a part in the Sunday night meets if I am home alone but it's not a regular event for me. Next time I get chance to join I'll ask how many lads describe themselves as straight.
I remember a guy answering a similar post by saying that it either wasn't a straight/ gay/ bi thing it was a "Male thing" or a "Cock thing", I can't remember which but it summed up the collective vibe that occurs sometimes when all the guys get deeply into the bate. Like a supportive collective trance.